Secondary battery and method for restoring capacity of secondary battery

ABSTRACT

An exterior body of a secondary battery includes an insertion portion for insertion of a third electrode including metal lithium. An injection and expelling portion through which an electrolyte solution can be replaced is further provided. Specifically, a nonaqueous secondary battery includes a positive electrode, a negative electrode, an electrolyte solution, a separator, and an exterior body covering the positive electrode, the negative electrode, and the electrolyte solution. The exterior body includes a positive electrode terminal to which the positive electrode is electrically connected, a negative electrode terminal to which the negative electrode is electrically connected, and an insertion portion for insertion of a third electrode including metal lithium.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object (a product including amachine, a manufacture, and a composition of matter) and a method (aprocess including a simple method and a production method). Inparticular, one embodiment of the present invention relates to anonaqueous secondary battery, or relates to a method for restoring acapacity of a nonaqueous secondary battery.

2. Description of the Related Art

Lithium-ion secondary batteries have advantageous effects such as highoutput and high energy density and have been frequently used for avariety of uses such as portable electronic devices, next-generationclean energy vehicles including hybrid electric vehicles (HEVs) andelectric vehicles (EVs), and stationary power storage devices. Inparticular, development of comparatively large-sized secondary batteriesfor vehicles and stationary power storage devices, which can be used fora long period of time, has been needed along with a growing demand forenergy saving in recent years.

A lithium-ion secondary battery, which is one of nonaqueous secondarybatteries, includes a positive electrode, a negative electrode, aseparator, a nonaqueous electrolyte solution, and an exterior bodycovering these components. In lithium-ion secondary batteries, positiveelectrodes and negative electrodes are generally used; the positiveelectrodes each include a positive electrode current collector made ofaluminum or the like and a positive electrode mix which includes apositive electrode active material capable of occluding and releasinglithium ions and which is applied to both surfaces of the positiveelectrode current collector, and the negative electrodes each include anegative electrode current collector made of copper or the like and anegative electrode mix which includes a negative electrode activematerial capable of occluding and releasing lithium ions and which isapplied to both surfaces of the negative electrode current collector.These positive and negative electrodes are insulated from each other bya separator provided therebetween, and the positive electrode and thenegative electrode are electrically connected to a positive electrodeterminal and a negative electrode terminal, respectively, which areprovided for the exterior body. The exterior body has a certain shapesuch as a cylindrical shape or a rectangular shape.

When a secondary battery is used for a long period of time, e.g., forseveral years or for more than ten years or more, a problem of adecrease in capacity arises. A cause of the decrease in the capacity ofa lithium-ion secondary battery is a reduction in lithium ionscontributing to a battery reaction.

There are several causes of the reduction in lithium ions contributingto a battery reaction. One of them is formation of a coating film on asurface of a negative electrode. Specifically, an electrolyte solutionis decomposed at the interface between the negative electrode and theelectrolyte solution, and a coating film containing lithium is formed ona surface of the negative electrode. Formation of the coating filmallows a stable battery reaction; however, excessive formation of thecoating film is not preferable because lithium ions contributing to abattery reaction are reduced.

The following is another cause of the reduction in lithium ionscontributing to a battery reaction. By rapid charging or the like, metallithium is deposited on an active material and a surface of an activematerial and separated from a current collector.

In normal low-rate charging, metal lithium is deposited on an activematerial and a surface of an active material. In the case whereconductivity is kept between the active material and the metal lithium,the deposited metal lithium slowly disappears in discharging. However,the metal lithium expands and shrinks when the active material,particularly the negative electrode active material, occludes andreleases a lithium ion. Therefore, when rapid charging is performed ordeposition of metal lithium is repeatedly performed for a long period oftime, the deposited metal lithium loses its conductivity with thecurrent collector, leading to separation of the metal lithium in somecases.

The separated active material or metal lithium causes clogging of theseparator, whereby the diffusibility of lithium ions is reduced andlithium ions are concentrated in the periphery of the clogging, leadingto further deposition of metal lithium and a further decrease in thecapacity of the secondary battery.

Another cause of the decrease in the capacity of a lithium-ion secondarybattery is deterioration of an electrolyte solution. An electrolytesolution which normally functions is reduced by decomposition of theelectrolyte solution at the interface between an electrode and theelectrolyte solution, vaporization of the electrolyte solution due toheat generated in a battery reaction, and the like, reducing thediffusibility of lithium ions.

The reduction in the diffusibility of lithium ions causes furtherdeposition of metal lithium as described above, leading to a viciouscycle.

In order to suppress the above-described reduction in lithium ionscontributing to a battery reaction, various methods have been studied.For example, a method for predoping a negative electrode with lithiumbefore assembly of a secondary battery is known. As another method, ametal lithium electrode is provided in advance as a third electrodeinside a secondary battery, and lithium ions are supplied from the metallithium electrode when its capacity is decreased (Patent Document 1).Furthermore, in another method under study, a metal lithium electrodewhich has been installed in a cassette case is inserted into a secondarybattery to supply lithium ions when its capacity is decreased (PatentDocument 2).

REFERENCES Patent Documents

-   [Patent Document 1] Japanese Published Patent Application No.    2012-195055-   [Patent Document 2] Japanese Published Patent Application No.    2002-324585

SUMMARY OF THE INVENTION

However, in a structure where a metal lithium electrode is provided inadvance inside an exterior body of a secondary battery as disclosed inPatent Document 1, there is a concern that metal lithium soaked in anelectrolyte solution for a long period of time may deteriorate.

Metal lithium reacts with water easily. Hence, in a method in which ametal lithium electrode installed in a cassette case is inserted asdisclosed in Patent Document 2, an insertion operation needs to beperformed in a dry room, which is unfavorable because it increases thecost of maintenance.

Another cause of the decrease in capacity of a secondary battery isdeterioration of an electrolyte solution as described above.

Thus, one object of one embodiment of the present invention is toprovide a secondary battery to which lithium can be supplied more easilyfrom the outside when its capacity is decreased. Another object is toprovide a secondary battery whose electrolyte solution can be replacedwhen its capacity is decreased. Another object is to restore a capacityof a secondary battery by supplying lithium from the outside andreplacing an electrolyte solution when its capacity is decreased.

In order to achieve any of the above objects, in one embodiment of thepresent invention, an insertion portion for insertion of a thirdelectrode including metal lithium is provided in an exterior body of asecondary battery. Furthermore, an injection and expelling portionthrough which an electrolyte solution can be replaced is provided.

One embodiment of the present invention is a nonaqueous secondarybattery including a positive electrode, a negative electrode, aseparator, an electrolyte solution, and an exterior body covering thepositive electrode, the negative electrode, the separator, and theelectrolyte solution; the exterior body includes a positive electrodeterminal to which the positive electrode is electrically connected, anegative electrode terminal to which the negative electrode iselectrically connected, and an insertion portion for insertion of athird electrode including metal lithium.

Another embodiment of the present invention is a nonaqueous secondarybattery including a positive electrode, a negative electrode, aseparator, an electrolyte solution, and an exterior body covering thepositive electrode, the negative electrode, the separator, and theelectrolyte solution; the exterior body includes a positive electrodeterminal to which the positive electrode is electrically connected, anegative electrode terminal to which the negative electrode iselectrically connected, an insertion portion for insertion of a thirdelectrode including metal lithium, and an electrolyte solution injectionand expelling portion through which the electrolyte solution can beinjected or expelled.

In any of the above, it is preferable that the nonaqueous secondarybattery be assumed to be installed in at least one installationdirection, a groove having a surface parallel to a surface of thepositive electrode and a surface of the negative electrode be providedin at least a part of the separator, and the longitudinal direction ofthe groove be perpendicular to a horizontal surface when the nonaqueoussecondary battery is installed in the installation direction.

Another embodiment of the present invention is a method for restoring acapacity of a nonaqueous secondary battery including a positiveelectrode, a negative electrode, a separator, an electrolyte solution,and an exterior body covering the positive electrode, the negativeelectrode, the separator, and the electrolyte solution, including thesteps of detecting a decrease in capacity of the secondary battery usinga detection means and increasing the amount of lithium in the whole ofthe secondary battery in such a manner that a third electrode includingmetal lithium is inserted through the insertion portion provided for theexterior body and a voltage is applied to the third electrode includingthe metal lithium and the negative electrode to transfer a lithium ionfrom the third electrode including the metal lithium to the negativeelectrode.

Another embodiment of the present invention is a method for restoring acapacity of a nonaqueous secondary battery including a positiveelectrode, a negative electrode, a separator, an electrolyte solution,and an exterior body covering the positive electrode, the negativeelectrode, the separator, and the electrolyte solution, including thesteps of detecting a decrease in capacity of the secondary battery usinga detection means and increasing the amount of lithium in the whole ofthe secondary battery in such a manner that a third electrode includingmetal lithium is inserted through the insertion portion provided in theexterior body and a voltage is applied to the third electrode includingthe metal lithium and the positive electrode to transfer a lithium ionfrom the third electrode including the metal lithium to the positiveelectrode.

Another embodiment of the present invention is a method for restoring acapacity of a nonaqueous secondary battery including a positiveelectrode, a negative electrode, a separator, an electrolyte solution,and an exterior body covering the positive electrode, the negativeelectrode, the separator, and the electrolyte solution, including thesteps of detecting a decrease in a capacity of the secondary batteryusing a detection means, replacing the electrolyte solution through aninsertion portion provided for the exterior body, and increasing theamount of lithium in the whole of the secondary battery in such a mannerthat a third electrode including metal lithium is inserted through theinsertion portion provided for the exterior body and a voltage isapplied to the third electrode including the metal lithium and one ofthe negative electrode and the positive electrode to transfer a lithiumion from the third electrode including the metal lithium to one of thenegative electrode and the positive electrode.

In one embodiment of the present invention, a secondary battery to whichlithium can be supplied more easily from the outside when its capacityis decreased can be provided, a secondary battery whose electrolytesolution can be replaced when its capacity is decreased can be provided,or a capacity of a secondary battery can be restored by supplyinglithium from the outside and replacing an electrolyte solution when itscapacity is decreased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a secondary battery of one embodiment of thepresent invention.

FIGS. 2A to 2C illustrate a method for restoring a capacity of asecondary battery of one embodiment of the present invention.

FIGS. 3A to 3D illustrate a secondary battery of one embodiment of thepresent invention and a method for restoring a capacity of the secondarybattery.

FIGS. 4A to 4E illustrate a secondary battery of one embodiment of thepresent invention.

FIGS. 5A to 5G illustrate a secondary battery of one embodiment of thepresent invention.

FIGS. 6A and 6B illustrate a method for restoring a capacity of asecondary battery of one embodiment of the present invention.

FIG. 7 illustrates an electrical device and a power storage device.

FIGS. 8A and 8B illustrate a power storage system.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawings. Note that the presentinvention is not limited to the description in these embodiments, and itis easily understood by those skilled in the art that modes and aspectsof the present invention can be modified in various ways. Accordingly,the present invention should not be interpreted as being limited to thecontent of the embodiments below.

Note that in each drawing described in this specification, the size ofeach component, such as the thickness and the size of a positiveelectrode, a negative electrode, an active material layer, an exteriorbody, an insertion portion, an injection and expelling portion, and thelike is exaggerated for clarity in some cases. Therefore, each componentis not necessarily limited to that size and not necessarily limited insize relative to another component.

Ordinal numbers such as “first”, “second”, and “third” are used forconvenience and do not denote the order of steps or the stacking orderof layers. Therefore, for example, description can be made even when“first” is replaced with “second” or “third”, as appropriate. Inaddition, the ordinal numbers in this specification and the like are notnecessarily the same as those which specify one embodiment of thepresent invention.

Note that in the structures of the present invention described in thisspecification and the like, the same portions or portions having similarfunctions in different drawings are denoted by the same referencenumerals, and description of such portions is not repeated. Further, thesame hatching pattern is applied to portions having similar functions,and the portions are not especially denoted by reference numerals insome cases.

Note that in this specification and the like, a charging rate C refersto the rate at which a secondary battery is charged. For example, thecharging rate in the case of charging a battery having a capacity of 1Ah with 1 A is 1 C. In addition, a discharging rate C refers to the rateat which a secondary battery is discharged. For example, the dischargingrate in the case of discharging a battery having a capacity of 1 Ah with1 A is 1 C.

The descriptions in embodiments for carrying out the invention can becombined with each other as appropriate.

Embodiment 1

In this embodiment, an example of a nonaqueous secondary battery of oneembodiment of the present invention is described with reference to FIGS.1A and 1B, FIGS. 2A to 2C, FIGS. 3A to 3D, FIGS. 4A to 4E, FIGS. 5A to5G, and FIGS. 6A and 6B.

<Secondary Battery>

First, an example of an exterior body of a secondary battery of oneembodiment of the present invention is mainly described with referenceto FIGS. 1A and 1B. FIG. 1A is a perspective view of a secondary battery100. FIG. 1B shows a part of a cross-sectional structure taken alongdashed-dotted line X1-X2 in FIG. 1A. The secondary battery 100 includesa positive electrode 101, a negative electrode 105, a separator 103between the positive electrode 101 and the negative electrode 105, andan electrolyte solution 107. The secondary battery 100 further includesan exterior body 109 covering the positive electrode 101, the negativeelectrode 105, the separator 103, and the electrolyte solution 107. InFIGS. 1A and 1B, the positive electrode 101, the separator 103, and thenegative electrode 105 are not shown in detail but are collectivelyindicated by a box for simplification of the drawings. The details ofthe positive electrode 101, the separator 103, and the negativeelectrode 105 will be described with reference to FIGS. 5A to 5G andFIGS. 6A and 6B.

The exterior body 109 includes a positive electrode terminal 113 towhich the positive electrode 101 is electrically connected, a negativeelectrode terminal 111 to which the negative electrode 105 iselectrically connected, and an insertion portion 115 for insertion of athird electrode 117 including metal lithium, which is to be describedlater. The exterior body 109 may be formed of a combination of an upperexterior body 109 a, a side exterior body 109 b, and a lower exteriorbody 109 c. As shown in FIG. 1B, the upper exterior body 109 a and theside exterior body 109 b are preferably crimped. Similarly, the sideexterior body 109 b and the lower exterior body 109 c are preferablycrimped.

The insertion portion 115 is preferably formed using a material havingelasticity. Here, the material having elasticity refers to a materialhaving a high elastic limit. Examples of the material having elasticityinclude various kinds of synthetic rubber such as NBR, SBR,fluororubber, and silicone rubber, natural rubber, plastic such as anacrylic copolymer, a structure using a carbon nanotube, and a compositematerial of any of these.

For example, the positive electrode terminal 113, the negative electrodeterminal 111, and the insertion portion 115 can be provided for theupper exterior body 109 a by outsert molding, though there is noparticular limitation on a method for forming the positive electrodeterminal 113, the negative electrode terminal 111, and the insertionportion 115.

As shown in FIG. 1B, the insertion portion 115 may have a structureincluding a space inside. Such a structure can prevent leakage of theelectrolyte solution and mixing of the atmospheric air into the exteriorbody at the time of inserting the third electrode 117 to be describedlater.

It is preferable that the positive electrode 101, the separator 103, andthe negative electrode 105 be formed in a region except a part of aspace under the insertion portion 115 so that a space that is necessaryfor the insertion of the third electrode 117 described later isobtained.

<Lithium Ion Supply Method>

An example of a lithium ion supply method, which is a method forrestoring a capacity of a secondary battery of one embodiment of thepresent invention, is described with reference to FIGS. 2A to 2C. In oneembodiment of the present invention, the third electrode 117 includingmetal lithium 117 a is inserted through the insertion portion 115, and alithium ion is supplied from the metal lithium 117 a to the positiveelectrode 101 or the negative electrode 105 to restore the capacity ofthe secondary battery 100.

Specifically, first, a decrease in the capacity of the secondary battery100 is detected using a detecting unit. The decrease in the capacity ofthe secondary battery 100 can be detected by measuring a current and avoltage during charge and discharge.

In the case where the capacity of the secondary battery is decreased, alithium ion is supplied to the positive electrode 101 or the negativeelectrode 105. Before the supply of the lithium ion, the third electrode117 including the metal lithium 117 a is prepared as shown in FIG. 2A.The metal lithium 117 a is provided inside an outer tube 117 c of thethird electrode 117. With such a structure where the metal lithium 117 ais provided inside the outer tube 117 c, the metal lithium 117 a can beprevented from contacting the atmospheric air. The outer tube 117 c hasa needle-like end which is capable of puncturing the insertion portion115. An inner tube 117 d is electrically connected to the metal lithium117 a to function as a terminal of the third electrode 117. The outertube 117 c is preferably provided with a stopper 117 b with which thedepth of the insertion of the third electrode 117 is controlled.

Then, as shown in FIG. 2B, the third electrode 117 is inserted throughthe insertion portion 115, and the inner tube 117 d is pressed downward,whereby the metal lithium 117 a and the electrolyte solution 107 aremade to be in contact with each other. Furthermore, the third electrode117 and the negative electrode terminal 111 are electrically connectedto each other via a resistor 119. Thus, lithium ions are dissolved inthe electrolyte solution 107 from the metal lithium 117 a of the thirdelectrode 117 and supplied to the negative electrode 105.

By the supply of lithium ions from the metal lithium 117 a to thenegative electrode 105, the amount of lithium in the whole of thesecondary battery 100 can be increased, so that the capacity of thesecondary battery 100 can be restored.

The resistor 119 preferably includes a semi-fixed resistor. An ammeteris preferably connected between the third electrode 117 and the negativeelectrode terminal 111 to monitor a current between the third electrode117 and the negative electrode terminal 111. The current is greatlylowered as time passes from the start of the supply of lithium ions. Thesupply of lithium ions is preferably completed when the current betweenthe third electrode 117 and the negative electrode terminal 111 reachesa predetermined value (e.g., approximately a tenth of a current value atthe start of the supply of lithium ions).

As shown in FIG. 2C, the third electrode 117 and the positive electrodeterminal 113 may be electrically connected to each other via theresistor 119, whereby lithium ions are dissolved in the electrolytesolution 107 from the metal lithium 117 a of the third electrode 117 andsupplied to the positive electrode 101. Accordingly, in a similarmanner, the amount of lithium in the whole of the secondary battery 100can be increased, and the capacity of the secondary battery 100 can berestored. In the case where lithium ions are supplied to the positiveelectrode 101, a voltmeter is preferably provided between the thirdelectrode 117 and the positive electrode 101. The supply of lithium ionsto the positive electrode 101 is preferably completed when a voltagebetween the third electrode 117 and the positive electrode 101 reaches apredetermined value (e.g., 2 V or lower).

Note that, generally, a potential difference between the positiveelectrode 101 and the metal lithium 117 a is larger than a potentialdifference between the negative electrode 105 and the metal lithium 117a. Thus, the supply of lithium ions takes a shorter time in the case ofsupplying lithium ions to the positive electrode 101 as shown in FIG. 2Cthan in the case of supplying lithium ions to the negative electrode 105as shown in FIG. 2B. For example, in the case of supplying lithium ionsto the negative electrode 105, the third electrode 117 needs to becontinuously inserted for 5 to 10 hours because an estimated chargingrate thereof is approximately 0.1 C to 0.2 C. In contrast, in the caseof supplying lithium ions to the positive electrode 101, the thirdelectrode 117 needs to be inserted for only approximately 1 hour becausean estimated charging rate thereof is approximately 1 C.

When the secondary battery 100 has a large capacity, a protectioncircuit is preferably provided between the third electrode 117 and oneof the negative electrode terminal 111 and the positive electrodeterminal 113 to prevent the supply of an excess amount of lithium ions.

<Variations of Third Electrode>

Note that the third electrode 117 is not limited to the structure shownin FIGS. 2A to 2C. For example, as shown in FIG. 3A, the third electrode117 may include a cover 117 f for covering the end of the outer tube 117c. The inside of the cover 117 f is preferably filled with an inert gas117 e to suppress deterioration of the metal lithium 117 a. Argon or thelike can be used for the inert gas 117 e. The cover 117 f is preferablyformed using a material having elasticity, more preferably formed usinga material having both elasticity and a water vapor barrier property. Asthe material of the cover 117 f, a various kinds of synthetic rubbersuch as silicone rubber, natural rubber, polypropylene, or poly(vinylchloride), or a composite material of any of these can be used.

The third electrode 117 shown in FIG. 3A is inserted through theinsertion portion 115 and the inner tube 117 d is pressed downward asshown in FIG. 3B, whereby the metal lithium 117 a and the electrolytesolution 107 are made to be in contact with each other. The thirdelectrode 117 and one of the negative electrode terminal 111 and thepositive electrode terminal 113 are electrically connected to each othervia the resistor 119. Thus, lithium ions can be dissolved in theelectrolyte solution 107 from the metal lithium 117 a of the thirdelectrode 117 and supplied to the negative electrode 105 or the positiveelectrode 101.

As shown in FIG. 3C, the inside of the outer tube 117 c of the thirdelectrode 117 may be filled with an electrolyte solution 117 g. With thethird electrode 117 having such a structure, the metal lithium 117 a andthe electrolyte solution 107 of the secondary battery 100 can be made tobe in contact with each other as shown in FIG. 3D without moving theinner tube 117 d, so that lithium ions can be supplied to the negativeelectrode 105 or the positive electrode 101. In addition, a spacerequired for the insertion of the third electrode 117 is reduced;accordingly, a space for the positive electrode 101, the separator 103,and the negative electrode 105 can be increased.

<Replacement of Electrolyte Solution>

Lithium ions are supplied by inserting the third electrode 117 throughthe insertion portion 115. Furthermore, the electrolyte solution 107 maybe supplied or replaced through the insertion portion 115. The capacityof the secondary battery 100 can be restored also by the supply or thereplacement of the electrolyte solution 107.

Although there is no particular limitation on a method for replacing theelectrolyte solution, a syringe having a needle-like end similar to thatof the third electrode 117 may be used to expel and inject theelectrolyte solution, for example.

In order to replace the electrolyte solution 107 easily, the exteriorbody 109 may be provided with an electrolyte solution injection andexpelling portion 121 in addition to the insertion portion 115, as shownin FIG. 4A. With such a structure, the electrolyte solution can beexpelled through one of the insertion portion 115 and the electrolytesolution injection and expelling portion 121, and the electrolytesolution can be injected through the other.

The position of the electrolyte solution injection and expelling portion121 is not limited to the position shown in FIG. 4A. For example, theelectrolyte solution injection and expelling portion 121 may be provideddiagonal to the insertion portion 115 as shown in FIG. 4B.

As shown in FIG. 4C, the exterior body 109 may be provided with a gasinjection and expelling valve 123. An inert gas is injected into thesecondary battery 100 through the gas injection and expelling valve 123.With the pressure of the inert gas, an electrolyte solution can beexpelled through one of the insertion portion 115 and the electrolytesolution injection and expelling portion 121. An electrolyte solutioncan be injected through the other, and a gas can be expelled through thegas injection and expelling valve 123.

In the case where a space required for the insertion of the thirdelectrode can be small, for example, in the case of using the thirdelectrode 117 as shown in FIG. 3D, a space for the positive electrode101, the separator 103, and the negative electrode 105 can be increasedaccordingly as shown in FIG. 4D.

An electrolyte solution which has deteriorated may be expelled throughthe insertion portion 115 or the electrolyte solution injection andexpelling portion 121 and injected again after filtration or the like.FIG. 4E illustrates an example of an electrolyte solution filtrationsystem 200.

The filtration system 200 includes a tank 201, a server 207, a pump 209,and a filter 211. When the electrolyte solution 107 of the secondarybattery 100 needs to be replaced because of deterioration, the tank 201is connected to the gas injection and expelling valve 123 of thesecondary battery 100. The electrolyte solution injection and expellingportion 121 is connected to the server 207. The insertion portion 115 isconnected to the filter 211. These connections are made via respectivevalves 203, 205, and 206. The valve 205 connecting the electrolytesolution injection and expelling portion 121 and the server 207 and thevalve 206 connecting the insertion portion 115 and the filter 211 arepreferably one-way valves in order to prevent the electrolyte solutionfrom flowing backward. The server 207 is preferably provided with avalve 213 for pressure adjustment.

The electrolyte solution 107 can be replaced in the following manner,for example. First, a gas in the tank 201 is injected into the exteriorbody 109, so that the electrolyte solution 107 in the exterior body 109is expelled to the server 207 with the pressure of the gas. Theelectrolyte solution expelled to the server 207 passes through thefilter 211 via the pump 209. The filter 211 can remove an unnecessarysubstance (e.g., particles which are separated from the positiveelectrode 101 or the negative electrode 105 and do not contribute tocharge and discharge, a polymerized substance of an organic solventincluded in the electrolyte solution, or the like) from an electrolytesolution which has deteriorated. After passing through the filter 211,the electrolyte solution is injected into the exterior body 109 again.The gas in the exterior body 109 at this time is expelled through thegas injection and expelling valve 123.

Although not shown, the electrolyte solution having passed through thefilter 211 may be injected into the exterior body 109 after being mixedwith a new electrolyte solution, a new electrolyte, or a new solvent.

<Separator>

In order to increase the diffusibility of lithium ions, the separator103 of the secondary battery 100 preferably includes a groove having asurface parallel to a surface of the positive electrode 101 and asurface of the negative electrode 105. Examples of the structure of theseparator 103 are described with reference to FIGS. 5A to 5G. Theseparator has minute pores, projected portions, or depressed portions.

FIG. 5A illustrates the positive electrode 101, the negative electrode105, and the separator 103 between the positive electrode 101 and thenegative electrode 105. The secondary battery 100 having this structureis assumed to be installed such that the largest surfaces of thepositive electrode 101 and the negative electrode 105 are perpendicularto a horizontal surface, for example, as shown in FIG. 5B. The secondarybattery 100 may be installed horizontally.

It is effective to increase the capability of the electrolyte solution107 to transfer lithium ions in increasing the diffusibility of lithiumions. Furthermore, heat is generated from the positive electrode 101 andthe negative electrode 105 by charge and discharge of the secondarybattery 100. As the capacity or output of the secondary battery 100increases, the amount of heat generation increases; excessive heat mightaccelerate deterioration of the electrolyte solution.

The secondary battery 100 including the separator 103 having a pluralityof grooves as shown in FIG. 5A is effective in improving the capabilityto transfer lithium ions or in releasing heat. In other words, theseparator has a projected portion between the grooves as shown in FIG.5A. The groove in the separator 103 is larger than the minute pore whichis provided in the separator. The grooves in the separator 103 areprovided in the form of stripes by pressing or the like. The grooves inthe separator 103 are provided on the side close to the positiveelectrode 101. The grooves in the separator 103 promote convection inthe electrolyte solution as indicated by arrows in FIG. 5B, for example.Specifically, the electrolyte solution heated by the positive electrode101 and the negative electrode 105 moves upward along the grooves in theseparator 103 to the vicinity of the exterior body 109. The electrolytesolution 107 in the vicinity of the exterior body 109 is cooled down andmoves downward along the inner wall of the exterior body 109. In otherwords, the grooves in the separator 103 serve as flow paths for theelectrolyte solution.

By promotion of convection in the electrolyte solution 107 in the abovemanner, the diffusibility of lithium ions is improved. Furthermore, bypromotion of convection in the electrolyte solution 107, the release ofheat is promoted, and the temperature of the separator is made uniform.Thus, deposition of a lithium metal can be suppressed. By promotion ofrelease of heat, deterioration of the electrolyte solution can besuppressed.

With the grooves serving as flow paths of the electrolyte solution, theelectrolyte solution 107 can be replaced more smoothly in the case ofreplacing the electrolyte solution 107.

FIGS. 5C to 5G illustrate other examples of the structure of theseparator 103.

In FIG. 5A, the groove in the separator 103 is formed so that thelongitudinal direction of the groove is perpendicular to the horizontalsurface, but the structure of the separator 103 is not limited thereto.As shown in FIG. 5C, the separator 103 may have a plurality of groovesin a perpendicular direction and a plurality of grooves in a horizontaldirection that cross each other. The separator 103 may have a pluralityof depressed portions as shown in FIGS. 5D and 5E. The separator 103 mayhave a plurality of serpentine grooves as shown in FIG. 5F. Theseparator 103 may have a plurality of grooves on both sides as shown inFIG. 5G. Furthermore, a separator having a structure formed by acombination of any of the above-described characteristics may be used.

Note that the grooves or depressed portions of the separator 103, i.e.,the flow paths for the electrolyte solution 107, are preferably formedso as to be perpendicular to an installation direction of the secondarybattery 100, in which case the grooves or depressed portions are moreeffective in promoting convection.

Although FIGS. 5A to 5G illustrate examples in which the separator 103is provided with grooves or depressed portions, one embodiment of thepresent invention is not limited to these examples. In some cases ordepending on the situation, the separator 103 may have a flat plateshape without grooves or depressed portions.

<Electrode>

Examples of the shape of the positive electrode 101 and the shape of thenegative electrode 105 that are included in the secondary battery 100are described with reference to FIGS. 6A and 6B.

In order to increase the capacity of the secondary battery 100, the areaof the positive electrode 101 and the area of the negative electrode 105are preferably large. For example, as shown in FIG. 6A, a plurality ofpositive electrodes 101 and a plurality of negative electrodes 105 maybe stacked with each other with separators 103 provided therebetween.The structure including a stack of the plurality of electrodes cansuppress separation of an active material from a current collector dueto expansion and shrink at the time when the active material occludesand releases lithium ions.

As shown in FIG. 6B, the positive electrode 101, the negative electrode105, and the separators 103 that are long and thin may be wound. Thewound electrodes can be manufactured by a simple process.

Embodiment 2

In this embodiment, examples of components including the positiveelectrode 101, the negative electrode 105, the electrolyte solution 107,and the separator 103 of the nonaqueous secondary battery 100 of oneembodiment of the present invention are described.

<Positive Electrode>

First, the positive electrode 101 is described.

The positive electrode 101 includes a positive electrode currentcollector and a positive electrode active material layer formed over thepositive electrode current collector by a coating method, a CVD method,a sputtering method, or the like, for example.

The positive electrode current collector can be formed using a materialthat has high conductivity and is not alloyed with lithium, such as ametal typified by stainless steel, gold, platinum, zinc, iron, copper,aluminum, or titanium, or an alloy thereof. Alternatively, an aluminumalloy to which an element which improves heat resistance, such assilicon, titanium, neodymium, scandium, or molybdenum, is added can beused. Still alternatively, a metal element which forms silicide byreacting with silicon can be used. Examples of the metal element whichforms silicide by reacting with silicon include zirconium, titanium,hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten,cobalt, nickel, and the like. The positive electrode current collectorcan have a foil shape, a plate (sheet) shape, a net shape, apunching-metal shape, an expanded-metal shape, or the like asappropriate. The positive electrode current collector preferably has athickness of greater than or equal to 10 μm and less than or equal to 30μm.

The positive electrode active material layer at least includes thepositive electrode active material, a conductive additive, and a binder.

Examples of the conductive additive are acetylene black (AB), ketjenblack, graphite (black lead) particles, and carbon nanotubes in additionto graphene described later.

The positive electrode active material is in the form of particles madeof secondary particles having average particle diameter and particlediameter distribution, which is obtained in such a way that materialcompounds are mixed at a predetermined ratio and baked and the resultingbaked product is crushed, granulated, and classified by an appropriatemeans.

As the positive electrode active material, a material into/from whichlithium ions can be inserted and extracted is used.

For example, an olivine-type lithium-containing material (LiMPO₄(general formula) (M is one or more of Fe(II), Mn(II), Co(II), andNi(II))) can be used. Typical examples of the general formula LiMPO₄ arelithium compounds such as LiFePO₄, LiNiPO₄, LiCoPO₄, LiMnPO₄,LiFe_(a)Ni_(b)PO₄, LiFe_(a)Co_(b)PO₄, LiFe_(a)Mn_(b)PO₄,LiNi_(a)Co_(b)PO₄, LiNi_(a)Mn_(b)PO₄ (a+b≦1, 0<a<1, and 0<b<1),LiFe_(c)Ni_(d)Co_(e)PO₄, LiFe_(c)Ni_(d)Mn_(e)PO₄,LiNi_(c)Co_(d)Mn_(e)PO₄ (c+d+e≦1, 0<c<1, 0<d<1, and 0<e<1), andLiFe_(f)Ni_(g)Co_(h)Mn_(i)PO₄ (f+g+h+i≦1, 0<f<1, 0<g<1, 0<h<1, and0<i<1).

Alternatively, a composite oxide material such as Li(_(2-j))MSiO₄(general formula) (M is one or more of Fe(II), Mn(II), Co(II), andNi(II); 0≦j≦2) may be used. Typical examples of the general formulaLi(_(2-j))MSiO₄ are compounds such as Li(_(2-j))FeSiO₄,Li(_(2-j))NiSiO₄, Li(_(2-j))CoSiO₄, Li(_(2-j))MnSiO₄,Li(_(2-j))Fe_(k)Ni_(l)SiO₄, Li(_(2-j))Fe_(k)Co_(l)SiO₄,Li(_(2-j))Fe_(k)Mn_(l)SiO₄, Li(_(2-j))Ni_(k)Co_(l)SiO₄,Li(_(2-j))Ni_(k)Mn_(l)SiO₄ (k+l≦1, 0<k<1, and 0<l<1),Li(_(2-j))Fe_(m)Ni_(n)Co_(q)SiO₄, Li(_(2-j))Fe_(m)Ni_(n)Mn_(q)SiO₄,Li(_(2-j))Ni_(m)Co_(n)Mn_(q)SiO₄ (m+n+q≦1, 0<m<1, 0<n<1, and 0<q<1), andLi(_(2-j))Fe_(r)Ni_(s)Co_(t)Mn_(u)SiO₄ (r+s+t+u≦1, 0<r<1, 0<s<1, 0<t<1,and 0<u<1).

Examples of a lithium-containing material with a layered rock-saltcrystal structure which can be used for the positive electrode activematerial include a lithium cobalt oxide (LiCoO₂); LiNiO₂; LiMnO₂;Li₂MnO₃; an NiCo-based lithium-containing material (a general formulathereof is LiNi_(x)Co_(1-x)O₂ (0<x<1)) such as LiNi_(0.8)Co_(0.2)O₂; anNiMn-based lithium-containing material (a general formula thereof isLiNi_(x)Mn_(1-x)O₂ (0<x<1)) such as LiNi_(0.5)Mn_(0.5)O₂; and anNiMnCo-based lithium-containing material (also referred to as NMC, and ageneral formula thereof is LiNi_(x)Mn_(y)Co_(1-x-y)O₂ (x>0, y>0, x+y<1))such as LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂.

Further alternatively, any of other various compounds, such as an activematerial having a spinel crystal structure (e.g., LiMn₂O₄) and an activematerial having an inverse spinel crystal structure (e.g., LiMVO₄) canbe used.

Still further alternatively, a solid solution containing any of theabove materials as an end-member can be used.

Note that a carbon layer may be provided on a surface of the positiveelectrode active material. With a carbon layer, conductivity of anelectrode can be increased. The positive electrode active material canbe coated with the carbon layer by mixing a carbohydrate such as glucoseat the time of baking the positive electrode active material.

In addition, the graphene which is added to the positive electrodeactive material layer as a conductive additive can be formed byperforming reduction treatment on graphene oxide.

Here, graphene in this specification includes single-layer graphene ormultilayer graphene including two to a hundred layers. Single-layergraphene refers to a one-atom-thick sheet of carbon molecules having πbonds. Graphene oxide refers to a compound formed by oxidation of suchgraphene. Note that when a graphene oxide is reduced to form a graphene,oxygen contained in the graphene oxide is not entirely released and partof oxygen remains in the graphene. When the graphene contains oxygen,the proportion of the oxygen, which is measured by X-ray photoelectronspectroscopy (XPS), is higher than or equal to 2 atomic % and lower thanor equal to 20 atomic %, preferably higher than or equal to 3 atomic %and lower than or equal to 15 atomic %.

In the case where graphene is multilayer graphene including grapheneobtained by reducing graphene oxide, the interlayer distance betweengraphenes is greater than or equal to 0.34 nm and less than or equal to0.5 nm, preferably greater than or equal to 0.38 nm and less than orequal to 0.42 nm, more preferably greater than or equal to 0.39 nm andless than or equal to 0.41 nm. In general graphite, the interlayerdistance of single-layer graphene is 0.34 nm. Since the interlayerdistance in the graphene used for the secondary battery of oneembodiment of the present invention is longer than that in the generalgraphite, lithium ions can easily transfer between layers of thegraphene in the multilayer graphene.

Graphene oxide can be formed by an oxidation method called a Hummersmethod, for example.

Note that graphene oxide has an epoxy group, a carbonyl group, acarboxyl group, a hydroxyl group, or the like. In graphene oxide in apolar solvent typified by NMP (also referred to as N-methylpyrrolidone,1-methyl-2-pyrrolidone, N-methyl-2-pyrrolidone, et cetera), oxygen in afunctional group is negatively charged; therefore, while interactingwith NMP, the graphene oxide repels other graphene oxide and is hardlyaggregated. Accordingly, in a polar solvent, graphene oxides can beeasily dispersed uniformly.

The length of one side (also referred to as a flake size) of thegraphene oxide is greater than or equal to 50 nm and less than or equalto 100 μm, preferably greater than or equal to 800 nm and less than orequal to 20 μm.

Unlike a conductive additive in the form of particles such as acetyleneblack, which makes point contact with a positive electrode activematerial, the graphene is capable of surface contact with low contactresistance; accordingly, the electron conductivity between the particlesof the positive electrode active material and the graphene can beimproved without an increase in the amount of a conductive additive.

The solvent is removed by volatilization from a dispersion medium inwhich the graphene oxide is uniformly dispersed, and the graphene oxideis reduced to give graphene; hence, pieces of the graphene remaining inthe positive electrode active material layer are partly overlapped witheach other and dispersed such that surface contact is made, thereby apath for electron conduction can be formed.

Thus, when graphene is used as a raw material and reduction of grapheneoxide is performed after formation of the electrode, graphene as aconductive additive is produced. Accordingly, the positive electrodeactive material layer with high electron conductivity can be formed.

The ratio of the positive electrode active material in the positiveelectrode active material layer can be increased because it is notnecessary to increase the added amount of the conductive additive inorder to increase contact points between the positive electrode activematerial and the graphene. Accordingly, the discharge capacity of thesecondary battery can be increased.

The average particle diameter of the primary particle of the positiveelectrode active material is less than or equal to 500 nm, preferablygreater than or equal to 50 nm and less than or equal to 500 nm. To makesurface contact with the plurality of particles of the positiveelectrode active material, the length of one side of the graphene isgreater than or equal to 50 nm and less than or equal to 100 μm,preferably greater than or equal to 800 nm and less than or equal to 20μm.

Examples of the binder included in the positive electrode activematerial layer are polyimide, polytetrafluoroethylene, polyvinylchloride, ethylene-propylene-diene polymer, styrene-butadiene rubber,acrylonitrile-butadiene rubber, fluorine rubber, polyvinyl acetate,polymethyl methacrylate, polyethylene, and nitrocellulose, in additionto polyvinylidene fluoride (PVDF) which is a typical example.

In the case where graphene is used as the conductive additive, it ispreferable that the proportions of the positive electrode activematerial, the graphene as the conductive additive, and the binder withrespect to the total weight of the positive electrode active materiallayer be greater than or equal to 90 wt % and less than or equal to 94wt %, greater than or equal to 1 wt % and less than or equal to 5 wt %,and greater than or equal to 1 wt % and less than or equal to 5 wt %,respectively.

<Negative Electrode>

Next, the negative electrode 105 of the secondary battery 100 will bedescribed.

The negative electrode 105 includes a negative electrode currentcollector and a negative electrode active material layer formed over thenegative electrode current collector by a coating method, a CVD method,a sputtering method, or the like, for example.

The negative electrode current collector can be formed using a materialthat has high conductivity and that is not alloyed with a carrier ionsuch as a lithium ion, e.g., stainless steel, gold, platinum, zinc,iron, copper, or titanium, or an alloy thereof. Alternatively, a metalelement which forms silicide by reacting with silicon can be used.Examples of the metal element which forms silicide by reacting withsilicon include zirconium, titanium, hafnium, vanadium, niobium,tantalum, chromium, molybdenum, tungsten, cobalt, nickel, and the like.The negative electrode current collector can have a foil shape, a plate(sheet) shape, a net shape, a punching-metal shape, an expanded-metalshape, or the like as appropriate. The negative electrode currentcollector preferably has a thickness of greater than or equal to 10 μmand less than or equal to 30 μm.

The negative electrode active material layer includes at least anegative electrode active material. Further, a conductive additive maybe also included.

There is no particular limitation on the material of the negativeelectrode active material as long as it is a material with which a metalcan be dissolved and deposited or a material into/from which metal ionscan be inserted and extracted. As the negative electrode activematerial, graphite, which is a carbon material generally used in thefield of power storage, can be used as well as metal lithium. Examplesof graphite include low crystalline carbon such as soft carbon and hardcarbon and high crystalline carbon such as natural graphite, kishgraphite, pyrolytic graphite, mesophase pitch based carbon fiber,meso-carbon microbeads (MCMB), mesophase pitches, petroleum-based coke,and coal-based coke.

As the negative electrode active material, other than the above carbonmaterials, an alloy-based material which enables a charge-dischargereaction by an alloying and dealloying reaction with carrier ions can beused. In the case where carrier ions are lithium ions, for example, amaterial containing at least one of Mg, Ca, Al, Si, Ge, Sn, Pb, As, Sb,Bi, Ag, Au, Zn, Cd, Hg, In, etc. can be used. Such metals have highercapacity than carbon. In particular, silicon has a significantly hightheoretical capacity of 4200 mAh/g. For this reason, silicon ispreferably used as the negative electrode active material.

The negative electrode active material layer may be formed by a coatingmethod in such a manner that a conductive additive and a binder areadded to the negative electrode active material to form a negativeelectrode paste and the negative electrode paste is applied onto thenegative electrode current collector and dried.

Note that the negative electrode active material layer may be predopedwith lithium. As a predoping method, a sputtering method may be used toform a lithium layer on a surface of the negative electrode activematerial layer. Alternatively, the negative electrode active materiallayer can be predoped with lithium by providing lithium foil on thesurface thereof.

Further, graphene is preferably formed on a surface of the negativeelectrode active material. In the case of using silicon as the negativeelectrode active material, the volume of silicon is greatly changed byocclusion and release of carrier ions in charge-discharge cycles.Therefore, adhesion between the negative electrode current collector andthe negative electrode active material layer is decreased, resulting indegradation of battery characteristics caused by charging anddischarging. In view of this, graphene is preferably formed on a surfaceof the negative electrode active material containing silicon becauseeven when the volume of silicon is changed in charge-discharge cycles,decrease in adhesion between the negative electrode current collectorand the negative electrode active material layer can be regulated, whichmakes it possible to reduce degradation of battery characteristics.

Graphene formed on the surface of the negative electrode active materialcan be formed by reducing graphene oxide in a similar manner to that ofthe method for forming the positive electrode. As the graphene oxide,the above-described graphene oxide can be used.

Further, a coating film of oxide or the like may be formed on thesurface of the negative electrode active material. A coating film formedby decomposition or the like of an electrolyte solution or the like incharging cannot release electric charges used at the formation, andtherefore forms irreversible capacity. In contrast, the coating film ofoxide or the like provided on the surface of the negative electrodeactive material in advance can reduce or prevent generation ofirreversible capacity.

As the film coating the negative electrode active material, an oxidefilm of any one of niobium, titanium, vanadium, tantalum, tungsten,zirconium, molybdenum, hafnium, chromium, aluminum, and silicon or anoxide film containing any one of these elements and lithium can be used.Such a film is denser than a conventional film formed on a surface of anegative electrode due to a decomposition product of an electrolytesolution.

For example, niobium oxide (Nb₂O₅) has a low electric conductivity of10⁻⁹ S/cm² and a high insulating property. For this reason, a niobiumoxide film inhibits electrochemical decomposition reaction between thenegative electrode active material and the electrolyte solution. On theother hand, niobium oxide has a lithium diffusion coefficient of 10⁻⁹cm²/sec and high lithium ion conductivity. Therefore, niobium oxide cantransmit lithium ions.

A sol-gel method can be used to coat the negative electrode activematerial with the coating film, for example. The sol-gel method is amethod for forming a thin film in such a manner that a solution of metalalkoxide, a metal salt, or the like is changed into a gel, which haslost its fluidity, by hydrolysis reaction and polycondensation reactionand the gel is baked. Since a thin film is formed from a liquid phase inthe sol-gel method, raw materials can be mixed uniformly on themolecular scale. For this reason, by adding a negative electrode activematerial such as graphite to a raw material of the metal oxide filmwhich is a solvent, the active material can be easily dispersed into thegel. In such a manner, the coating film can be formed on the surface ofthe negative electrode active material.

The use of the coating film can prevent a decrease in the capacity ofthe secondary battery.

<Electrolyte Solution>

As a solvent for the electrolyte solution 107 used in the secondarybattery 100, an aprotic organic solvent is preferably used. For example,one of ethylene carbonate (EC), propylene carbonate (PC), butylenecarbonate, chloroethylene carbonate, vinylene carbonate,γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethylcarbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methylacetate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane(DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile,benzonitrile, tetrahydrofuran, sulfolane, and sultone can be used, ortwo or more of these solvents can be used in an appropriate combinationin an appropriate ratio.

With the use of a gelled high-molecular material as the solvent of theelectrolyte solution, safety against liquid leakage and the like isimproved. Further, a secondary battery can be thinner and morelightweight. Typical examples of the high-molecular material aresilicone, polyacrylamide, polyacrylonitrile, polyethylene oxide,polypropylene oxide, a fluorine-based polymer, and the like.

Alternatively, the use of one or more of ionic liquids (room temperaturemolten salts) which are less likely to burn and volatilize as thesolvent for the electrolytic solution can prevent the secondary batteryfrom exploding or catching fire even when the secondary batteryinternally shorts out or the internal temperature increases due toovercharging or the like.

As an electrolyte dissolved in the above-described solvent, one oflithium salts such as LiPF₆, LiClO₄, LiAsF₆, LiBF₄, LiAlCl₄, LiSCN,LiBr, LiI, Li₂SO₄, Li₂B₁₀Cl₁₀, Li₂B₁₂Cl₁₂, LiCF₃SO₃, LiC₄F₉SO₃,LiC(CF₃SO₂)₃, LiC(C₂F₅SO₂)₃, LiN(CF₃SO₂)₂, LiN(C₄F₉SO₂)(CF₃SO₂), andLiN(C₂F₅SO₂)₂, or two or more of these lithium salts in an appropriatecombination in an appropriate ratio.

As the electrolyte of the electrolyte solution, a material containinglithium ions serving as carrier ions is used. Typical examples of theelectrolyte include lithium salts such as LiClO₄, LiAsF₆, LiBF₄, LiPF₆,and Li(C₂F₅SO₂)₂N.

Instead of the electrolytic solution, a solid electrolyte including aninorganic material such as a sulfide-based inorganic material or anoxide-based inorganic material, or a solid electrolyte including ahigh-molecular material such as a polyethylene oxide (PEO)-basedhigh-molecular material may alternatively be used. When the solidelectrolyte is used, it is not necessary to provide a separator.Further, the battery can be entirely solidified; therefore, there is nopossibility of liquid leakage and thus the safety of the battery isdramatically increased.

<Separator>

As a separator of the secondary battery, a porous insulator such ascellulose, polypropylene (PP), polyethylene (PE), polybutene, nylon,polyester, polysulfone, polyacrylonitrile, polyvinylidene fluoride, ortetrafluoroethylene can be used. Alternatively, nonwoven fabric of aglass fiber or the like, or a diaphragm in which a glass fiber and apolymer fiber are mixed may be used.

Embodiment 3

The secondary battery of one embodiment of the present invention can beused as a power source and a power storage device for a variety ofelectrical devices. The electrical devices may each include a secondarybattery or may be connected wirelessly or with a wiring to one or moresecondary batteries and a control device controlling power systems ofthese devices to form a power system network (electric power network).The electric power network controlled by the control device can improveusage efficiency of electric power in the whole network.

FIG. 7 illustrates an example of a home energy management system (HEMS)in which a plurality of home appliances, a control device, a secondarybattery, and the like are connected in a house. Such a system makes itpossible to check easily the power consumption of the whole house. Inaddition, the plurality of home appliances can be operated with a remotecontrol. Further, automatic control of the home appliances with a sensoror the control device can also contribute to low power consumption.

A panelboard 8003 set in a house 8000 is connected to an electric powersystem 8001 through a service wire 8002. The panelboard 8003 supplies ACpower which is electric power supplied from a commercial power sourcethrough the service wire 8002 to each of the plurality of homeappliances. A control device 8004 is connected to the panelboard 8003and also connected to the plurality of home appliances, a power storagesystem 8005, a solar power generation system 8006, and the like.Further, the control device 8004 can also be connected to an electricvehicle 8012 which is parked outside the house 8000 or the like andoperates independently of the panelboard 8003.

The control device 8004 connects the panelboard 8003 to the plurality ofhome appliances to form a network, and controls the plurality of homeappliances connected to the network.

In addition, the control device 8004 is connected to Internet 8011 andthus can be connected to a management server 8013 through the Internet8011. The management server 8013 receives data on the status of electricpower usage of users and therefore can create a database and can providethe users with a variety of services based on the database. Further, asneeded, the management server 8013 can provide the users with data onelectric power charge for a corresponding time zone, for example. On thebasis of the data, the control device 8004 can set an optimized usagepattern in the house 8000.

Examples of the plurality of home appliances are a display device 8007,a lighting device 8008, an air-conditioning system 8009, and an electricrefrigerator 8010 which are illustrated in FIG. 7. However, it isneedless to say that the plurality of home appliances are not limited tothese examples and refer to a variety of electrical devices which can beset inside a house, such as the above-described electrical devices.

In a display portion of the display device 8007, a semiconductor displaydevice such as a liquid crystal display device, a light-emitting deviceincluding a light-emitting element, e.g., an organic electroluminescent(EL) element, in each pixel, an electrophoretic display device, adigital micromirror device (DMD), a plasma display panel (PDP), or afield emission display (FED) is provided, for example. A display devicefunctioning as a display device for displaying information, such as adisplay device for TV broadcast reception, a personal computer,advertisement, and the like, is included in the category of the displaydevice 8007.

The lighting device 8008 includes an artificial light source whichgenerates light artificially by utilizing electric power in itscategory. Examples of the artificial light source are an incandescentlamp, a discharge lamp such as a fluorescent lamp, and a light-emittingelement such as a light emitting diode (LED) and an organic EL element.Although being provided on a ceiling in FIG. 7, the lighting device 8008may be installation lighting provided on a wall, a floor, a window, orthe like or desktop lighting.

The air-conditioning system 8009 has a function of adjusting an indoorenvironment such as temperature, humidity, and air cleanliness. FIG. 7illustrates an air conditioner as an example. The air conditionerincludes an indoor unit in which a compressor, an evaporator, and thelike are integrated and an outdoor unit (not illustrated) in which acondenser is incorporated, or an integral unit thereof.

The electric refrigerator 8010 is an electrical device for the storageof food and the like at low temperature and includes a freezer forfreezing at 0° C. or lower. A refrigerant in a pipe which is compressedby a compressor absorbs heat when vaporized, and thus inside theelectric refrigerator 8010 is cooled.

The plurality of home appliances may each include a secondary battery ormay use electric power supplied from the power storage system 8005 orthe commercial power source without including the secondary battery. Byusing a secondary battery as an uninterruptible power source, theplurality of home appliances each including the secondary battery can beused even when electric power cannot be supplied from the commercialpower source due to power failure or the like.

In the vicinity of a terminal for power supply in each of theabove-described home appliances, an electric power sensor such as acurrent sensor can be provided. Data obtained with the electric powersensor is sent to the control device 8004, which makes it possible forusers to check the used amount of electric power of the whole house. Inaddition, on the basis of the data, the control device 8004 candetermine the distribution of electric power supplied to the pluralityof home appliances, resulting in the efficient or economical use ofelectric power in the house 8000.

In a time zone when the usage rate of electric power which can besupplied from the commercial power source is low, the power storagesystem 8005 can be charged with electric power from the commercial powersource. Further, with the use of the solar power generation system 8006,the power storage system 8005 can be charged during the daytime. Notethat an object to be charged is not limited to the power storage system8005, and a secondary battery included in the electric vehicle 8012 andthe secondary batteries included in the plurality of home applianceswhich are connected to the control device 8004 may each be the object tobe charged.

Electric power stored in a variety of secondary batteries in such amanner is efficiently distributed by the control device 8004, resultingin the efficient or economical use of electric power in the house 8000.

As an example of controlling the electric power network, the example ofcontrolling an electric power network on a house scale is describedabove; however, the scale of the electric power network is not limitedthereto. An electric power network on an urban scale or a national scale(also referred to as a smart grid) can be created by a combination of acontrol device such as a smart meter and a communication network.Further, a microgrid which is on a scale of a factory or an office andincludes an energy supply source and a plant consuming electric power asunits can be constructed.

Next, an example of a power storage system in which the secondarybattery of one embodiment of the present invention is used is describedwith reference to FIGS. 8A and 8B. A power storage system 8100 to bedescribed here can be used at home as the power storage system 8005described above. Here, the power storage system 8100 is described as ahome-use power storage system as an example; however, it is not limitedthereto and can also be used for business use or other uses.

As illustrated in FIG. 8A, the power storage system 8100 includes a plug8101 for being electrically connected to a system power supply 8103.Further, the power storage system 8100 is electrically connected to apanelboard 8104 installed in home.

The power storage system 8100 may further include a display panel 8102for displaying an operation state or the like, for example. The displaypanel may have a touch screen. In addition, the power storage system8100 may include a switch for turning on and off a main power source, aswitch to operate the power storage system, and the like as well as thedisplay panel.

Although not illustrated, an operation switch to operate the powerstorage system 8100 may be provided separately from the power storagesystem 8100; for example, the operation switch may be provided on a wallin a room. Alternatively, the power storage system 8100 may be connectedto a personal computer, a server, or the like provided in home, in orderto be operated indirectly. Still alternatively, the power storage system8100 may be remotely operated using the Internet, an informationterminal such as a smartphone, or the like. In such cases, a mechanismthat performs wired or wireless communication between the power storagesystem 8100 and other devices is provided in the power storage system8100.

FIG. 8B illustrates an example of a circuit configuration of the powerstorage system 8100. The power storage system 8100 includes a secondarybattery group 8106 and a battery management system (BMS) 8108.

In the secondary battery group 8106, m secondary battery units 8109_1 to8109 _(—) m are connected in parallel. In each of the m secondarybattery units 8109_1 to 8109 _(—) m, n secondary batteries 8110_1 to8110 _(—) n are connected in series. The secondary battery of oneembodiment of the present invention can be used as each of the secondarybatteries 8110.

The BMS 8108 includes a battery management unit (BMU) 8107, and the BMU8107 has functions of monitoring, controlling, and protecting the stateof the secondary battery group 8106. For example, the BMU 8107 iselectrically connected to the secondary batteries 8110_1 to 8110 _(—) nincluded in the secondary battery group 8106 and can collect cellvoltage data. Each of the secondary batteries 8110_1 to 8110 _(—) n isprovided with a thermistor so that the cell temperature data can becollected.

The BMS 8108 includes an AC-DC inverter 8115 and a DC-AC inverter 8116.The AC-DC inverter 8115 is electrically connected to a plug 8101, andthe DC-AC inverter 8116 is electrically connected to an externalconnection terminal 8105. Charge and discharge of the power storagesystem 8100 are switched with a switch 8111 and a switch 8112. Instoring power in the power storage system 8100, for example, AC powerfrom the system power supply 8103 is converted into DC power, which istransmitted to the BMU 8107. In deriving power from the power storagesystem 8100, power stored in the secondary battery group 8106 isconverted into AC power, which is supplied to an indoor load, forexample. Note that the electric power may be supplied from the powerstorage system 8100 to the load through the panelboard 8104 asillustrated in FIG. 8A or may be directly supplied from the powerstorage system 8100 through wired or wireless transmission.

Note that a power source for charging the power storage system 8100 isnot limited to the system power supply 8103 described above; forexample, electric power may be supplied from a solar power generatingsystem installed outside or a power storage system mounted on anelectric vehicle.

The AC-DC inverter 8115 and the DC-AC inverter 8116 are connected toammeters 8113 and 8114, and the BMU 8107 can collect data from theammeters 8113 and 8114. Depending on these data, the BMU 8107 canmonitor overcharge and overdischarge, monitor overcurrent, control acell balancer, manage the deterioration condition of a battery,calculate the remaining battery level (the state of charge (SOC)),control a cooling fan of a driving secondary battery, or controldetection of failure, for example.

The BMU 8107 is connected to a data logger 8117, and the data logger8117 is connected to a ROM 8118. The data logger 8117 is connected to analarm 8119 or the like, and information of the power storage system 8100can be displayed on the display panel or the like 8102.

Note that the secondary batteries 8110_1 to 8110 _(—) m may have some ofor all the functions, or the secondary battery units 8109_1 to 8109 _(—)m may have the functions.

Note that, as an electronic circuit included in the BMU 8107, anelectronic circuit including the oxide semiconductor transistordescribed above is preferably provided. In this case, power consumptionof the BMU 8107 can be significantly reduced.

This application is based on Japanese Patent Application serial no.2013-102780 filed with Japan Patent Office on May 15, 2013, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A nonaqueous secondary battery comprising: apositive electrode; a negative electrode; a separator between thepositive electrode and the negative electrode; an electrolyte solution;and an exterior body surrounding the positive electrode, the negativeelectrode, the separator, and the electrolyte solution, wherein theexterior body comprises: a positive electrode terminal to which thepositive electrode is electrically connected; a negative electrodeterminal to which the negative electrode is electrically connected; andan insertion portion for insertion of a third electrode, the thirdelectrode comprising lithium.
 2. The nonaqueous secondary batteryaccording to claim 1, wherein the separator at least partly comprises adepression or a groove.
 3. The nonaqueous secondary battery according toclaim 1, wherein the separator at least partly comprises one of adepression and a groove, and wherein the one of the depression and thegroove is parallel to the positive electrode and the negative electrode.4. The nonaqueous secondary battery according to claim 1, wherein theseparator at least partly comprises one of a depression and a groove,and wherein the one of the depression and the groove is located in adirection perpendicular to an installation surface for the nonaqueoussecondary battery.
 5. The nonaqueous secondary battery according toclaim 1, wherein the exterior body further comprises a portion forinjection or expelling of the electrolyte solution.
 6. The nonaqueoussecondary battery according to claim 1, wherein the third electrodecomprises an inner tube configured to be electrically connected to oneof the positive electrode and the negative electrode.
 7. The nonaqueoussecondary battery according to claim 1, wherein the third electrodecomprises an outer tube having a needle-like shape.
 8. The nonaqueoussecondary battery according to claim 1, wherein the third electrodecomprises a stopper, and wherein the stopper is configured to control adepth of the third electrode in the electrolyte solution.
 9. Thenonaqueous secondary battery according to claim 1, wherein the thirdelectrode comprises a cover, and wherein an inside of the cover isfilled with an inert gas.
 10. A method for restoring a capacity of anonaqueous secondary battery, the nonaqueous secondary batterycomprising: a positive electrode; a negative electrode; a separatorbetween the positive electrode and the negative electrode; anelectrolyte solution; and an exterior body surrounding the positiveelectrode, the negative electrode, the separator, and the electrolytesolution, the exterior body comprising an insertion portion, the methodcomprising the steps of: inserting a third electrode to the insertionportion, the third electrode comprising lithium; and applying a voltageto the third electrode and one of the positive electrode and thenegative electrode to supply a lithium ion from the third electrode tothe one of the positive electrode and the negative electrode.
 11. Themethod for restoring a capacity of a nonaqueous secondary batteryaccording to claim 10, further comprising a step of detecting thecapacity of the nonaqueous secondary battery before inserting the thirdelectrode to the insertion portion.
 12. The method for restoring acapacity of a nonaqueous secondary battery according to claim 10,further comprising a step of injecting or expelling the electrolytesolution.
 13. The method for restoring a capacity of a nonaqueoussecondary battery according to claim 10, wherein lithium is inserted tothe insertion portion by using an inner tube and an outer tube.